The Roles of Principles in Enterprise Architecture

14 Pages·2010·0.19 MB·English

The Roles of Principles in Enterprise Architecture
H.A.Proper1,2andD.Greefhorst3
1 PublicResearchCentreHenriTudor,Luxembourg
2 RadboudUniversityNijmegen,Nijmegen,TheNetherlands
3 ArchiXL,Amersfoort,TheNetherlands
Abstract. Keyconceptsinenterprisearchitectureincludeconcerns,principles,
models,viewsandframeworks.Whilemostoftheseconceptshavereceivedam-
pleattentioninresearch,theconceptofprincipleshasnotbeenstudiedmuchyet.
Inthispaper,wethereforespecificallyfocusontheroleofprinciplesinthefield
ofenterprisearchitecture,wherewepositionenterprisearchitectureasameans
todirectenterprisetransformations.
Inpractice,manydifferenttypesofarchitectureprinciplesareused.Atthesame
time,principlesarereferredtobydifferentnames,includingarchitectureprinci-
ples,designprinciples,andITpolicies.Theprimarygoalofthispaperis,there-
fore,toarriveataconceptualframeworktomoreclearlyclarifyandpositionthese
differenttypes.
Thepaperstartswithadiscussiononenterprisearchitectureasameanstogovern
enterprise transformation. This provides a framework to position the different
typesofprinciples,andhighlighttheirrolesinenterprisetransformations.
1 Introduction
Asdiscussedin[1],keyconceptsinthefieldofenterprisearchitectureincludeconcerns,
principles, models, views and frameworks.Ampleresearchhas beenconductedonar-
chitectureframeworks,architecturemodellinglanguages[2,3],modelanalysis[4,5],
aswellasviewpointsandconcerns[6,7,8].Inthispaperweturnourfocustothecon-
ceptofprinciplesanditsroleinthefieldofenterprisearchitecture.Giventhatprinciples
havenotreceivedalotofresearchattention [9],thereisaneedtobetterunderstandtheir
essense.
Several approaches to enterprise architecture position principles as an important
ingredient [10, 11, 1, 12, 13], while some even go as far as to position principles as
beingtheessenceofarchitecture[14].Atthesametime,initialcasestudies[15,16,17,
18, 19, 20, 21, 22, 23, 24, 25] indicate there to be a wide variation in the actual use
ofprinciples.Theprimaryaimofthispaperisthereforetoarriveatafirstversionofa
conceptualframeworkwhichmoreclearlyidentifiesandpositionsthedifferenttypesof
principles.
Theframeworkpresentedinthispaperisthefirstiterationinadesignscience[26]
drivenresearcheffortinwhichweaimtomoreclearlydefinetheconceptofarchitecture
principles,anddevelopanassociatedmethodologyfordefininganddescribingarchitec-
tureprinciples.Thisfirstiteration,providesasynthesisofexistingviewsonenterprise
architectureandenterpriseengineering[27,1,14,13].
2 H.A.ProperandD.Greefhorst
Theremainderofthispaperisstructuredasfollows.Beforeweareabletosensibly
explore the different types of principles, and their roles in enterprise transformations,
Section 2 offers a review of our understanding of the fundamental purpose of archi-
tectureasameanstodirectenterprisetransformation.InSection3,wethenprovidea
conceptualframeworkofthedifferenttypesofprinciplesthatcanbediscernedwithin
ourfield.
2 Architectureasameanstogovernenterprisetransformations
Inlinewith[1],wetaketheperspectivethatenterprisearchitectureshouldplayapivotal
role in governing the continuous improvement process of an enterprise. In order to
better understand the governing role of enterprise architecture, this section positions
architectureasameanstogovernenterprisetransformations.Aswewillsee,principles
arethekeymeanstogovernthedirectionofthetransformationofanenterprise.
Inourview,governingenterprisetransformationsfirstandforemostentailstheper-
spective on an enterprise as a purposely designed and implemented artefact. This en-
ablesthegoverningsystemtogoverntheenterprisetransformationintermsofaclear
goal,itscurrentstate,andthedesiredfuturestatesoftheenterprise.Doingso,impliesa
perspectiveonproperlygovernedenterprisetransformationasbeingaformofengineer-
ing.Thisgivesrisetothefieldofenterpriseengineering[28,14],whichisanemerging
disciplinethatregardsthedesignandimplementationofenterprisesfromanengineer-
ingperspective.Twokeyparadigmsunderpinthisdiscipline.Thefirstparadigmstates
that enterprises are purposefully designed and implemented systems. Consequently,
theycanbere-designedandre-implementedifthereisaneedforchange.Thesecond
paradigmofenterpriseengineeringisthatenterprisesareprimarilysocialsystems,sup-
portedbytechnicalsystems.Thismeansthatthedominantsystemelementsaresocial
individuals,andthattheessenceofanenterprise’soperationliesintheenteringintoand
complyingwithcommitmentsbetweenthesesocialindividuals,whiletheimplementa-
tionofthisessenceinvolvesthedesignofanorchestratedcollaborationbetweensocial
beingsandtechnicalartefacts.
In line with [29, 1], the governance of an enterprise transformation process is re-
gardedasinvolvingaforce-fieldbetweenenterprisestrategy,programmemanagement
andenterprisearchitecture.Whenonlyconsideringthetypicalprojectparameters,one
runstheriskofconducting“localoptimisations”atthelevelofspecificprojects.Forex-
ample,whenmakingdesigndecisionswhichhaveanimpactthattranscendsaspecific
project, projects will still aim for solutions that provide the best cost/benefits trade-
off within the scope of that specific project while not looking at the overall picture.
Such local optimisations are likely to damage the overall quality of the result of the
transformation [1]. Enterprise architecture is concerned with an operationalisation of
the direction in which the enterprise aims to transform itself, in terms core properties
oftheenterprisebeingengineered.Thisoperationalisationallowsthedifferentchange
projectstobeassessedwhethertheycontributetotherealisationofthestrategy,while
guardingthepropertiesthattranscendspecificprojects.
Inthispaperwefocusonthepositionofenterprisearchitectureinrelationtoenter-
priseengineering,andthepotentialrolesofprincipleswithinthis.Fromthatcontextit
TheRolesofPrinciplesinEnterpriseArchitecture 3
isusefulltoseearchitectureas:thenormativerestrictionofdesignfreedom[14],allow-
ing enterprise architecture to exert its governing role towards the enterprise transfor-
mation.Itstressesanimportantgoalofarchitecture:torestrictdesignfreedom,which
canalsobeinterpretedas“toreducedesignstress”.Thisdoesnotexcludearchitecture
as a means for other goals. Indeed [2, 1] classifies architecture viewpoints into de-
signing,deciding,contractingandinformingviewpoints.Furthermore,in[1]enterprise
architecture is positioned explicitly as a means for informed governance of enterprise
transformation,requiringindicatorsandcontrolstogovernenterprisetransformations.
The desire to restrict design freedom implies normative instruments with which
suchrestrictionscanbemade.Webelievearchitectureprinciplesarekeyinstrumentsin
this[30],andwearecertainlynotaloneindoingso.Severalapproachespositionprinci-
plesasanimportantingredient[31,32,10,11,1,13,33,34],whilesomeevengoasfar
topositionprinciplesasbeingtheessenceofarchitecture[14].Architectureprinciples
fill the gap between high-level strategic intentions and concrete designs. They ensure
that the enterprise architecture is future directed, and can actually guide design deci-
sions, while preventing analysis paralysis by focussing on the essence. Furthermore,
they document fundamental choices in an accessible form, and ease communication
with all those affected. They are formulated based on drivers such as strategy, goals
and risks. Potential undesired impact on the goals of stakeholders can be reduced by
formulatingarchitectureprinciples.
3 Aconceptualframeworkforarchitectureprinciples
Asarguedbefore,wetaketheperspectivethatarchitectureprinciplesareacornerstone
ofenterprisearchitecture.Thegoalofthissection,istoprovideaconceptualframework
forarchitectureprinciples.Asmentionedbefore,theframeworkpresentedinthispaper
isthefirstiterationinadesignscience[26]drivenresearcheffortinwhichweendeavour
tomoreclearlydefinetheconceptofarchitectureprinciples,anddevelopanassociated
methodology for defining and describing architecture principles. The first iteration as
presentedinthispaper,providesasynthesisofexistingviewsonenterprisearchitecture
andenterpriseengineering[27,1,14,13].
3.1 History
ThetermprincipleissaidtooriginatefromtheLatinwordofprincipium[35],which
means “origin”, “beginning” or “first cause”. Vitruvius, an architect in ancient Rome,
usedprinciplestoexplainwhatistrueandindisputable,andshouldapplytoeveryone.
Vitruviusconsideredprinciplesastheelements,thelawsofnaturethatproducespecific
results. For instance, he observed how certain principles of the human body, such as
symmetryandproportion,ensure“perfection”.Thehumanbodywasagreatsourceof
inspirationtohim.Heevenbelievedthattheprinciplesofthehumanbodyshouldalso
be applied in the design of gardens and buildings because it would always lead to a
perfectresult:anultimatecombinationofbeauty,robustnessandusability.
When using principles in the sense of beginning, they generally provide insight
into the causes of certain effects. These causes can be laws of nature, beliefs or rules
4 H.A.ProperandD.Greefhorst
of conduct. Laws of nature simply are, and influence the things we do. Examples of
suchprinciplesarethelawofgravityandthePauliexclusionprinciple.Thelatterisa
quantummechanicalprincipleformulatedbyWolfgangPauliin1925.Itstatesthatno
two identical fermions may occupy the same quantum state simultaneously. Another
example, more directly relevant to enterprise engineering, is the principle of requisite
varietyfromgeneralsystemstheory,whichstatesthataregulatingsystemshouldmatch
thevarietyofthesystemthatshouldberegulated[36].
Beliefsaretypicallyfoundedinmoralvalues.ExamplesofsuchprinciplesareMar-
tin Luther King’s principles of nonviolence, that were to guide the civil rights move-
ment.Inanenterpriseengineeringcontext,examplesofsuchprincipleswouldbe:No
wrong doors (suggesting that clients should be helped at whichever office/desk they
approachtheenterprise)andThecustomerisalwaysright.
Rules of conduct are explicitly defined to influence behaviour, and are typically
basedonfactsandbeliefs.GeneralexamplesincludetheTenCommandmentsfromthe
Bible, e.g. “You shall not murder” and “You shall not commit adultery”. In our enter-
prise engineering context, examples would be: Clients can access the entire portfolio
ofservicesofferedbyanypartofthegovernmentbywayofallchannelsthroughwhich
government services are offered and Before delivering goods and services to external
parties,wemustholdreceiptoftheassociatedpayment.
The remainder of this section will show various dimensions in which principles
canbepositioned.Wedistinguishscientificprinciplesfromnormativeprinciples,posi-
tioningarchitectureprinciplesasnormativeprinciples.Wedividenormativeprinciples
into credos and norms, in which the latter form is needed in order to provide enough
restriction of design freedom. We show how principles relate to requirements and in-
structions. Finally, we position architecture as a form of essential design, focusing on
thefundamentalandessentialaspects[37].
3.2 Scientificprinciplesversusnormativeprinciples
TheAmericanEngineers’CouncilforProfessionalDevelopment[38]statesthatengi-
neeringconcerns“thecreativeapplicationofscientificprinciplestodesignordevelop
structures, machines, apparatus, or manufacturing processes, or works utilising them
...”.Principlesareusedinawiderangeofengineeringdisciplinessuchasindustrialen-
gineering,chemicalengineering,civilengineering,electricalengineeringandsystems
engineering.Theycanbeseenasaformofdesignknowledgethatshouldbeshared,in
ordertoincreasethequalityofdesigns.Inlinewith[38],wewillrefertotheseprinci-
plesasscientificprinciples.
Scientificprinciplesarelikelytobecross-disciplinaryinthesensethattheywillbe
applicableinvariousdesigndisciplines.Lidwell[39]providesalistof100“universal
principlesofdesign”,consistingoflaws,guidelines,humanbiases,andgeneraldesign
considerations.Theprinciplescanbeusedasaresourcetoincreasecross-disciplinary
knowledge and understanding of design, promote brainstorming and idea generation
fordesignproblems,formachecklistofdesignprinciples,andtocheckthequalityof
design processes and products. Examples of principles described by Lidwell that fall
into the category of scientific principles are the “exposure effect” and “performance
load”. The first principle states that “repeated exposure to stimuli for which people
TheRolesofPrinciplesinEnterpriseArchitecture 5
haveneutralfeelingswillincreasethelikeabilityofthestimuli”.Thelatterstates“the
greater the effort to accomplish a task, the less likely the task will be accomplished
successfully”.
Principleshavealwaysplayedanimportantroleincivilengineering,aprofessional
engineering discipline that deals with the design, construction and maintenance of
the physical and naturally built environment, including works such as bridges, roads,
canals,damsandbuildings.Principlesfromgeneralsystemstheory,suchastheearlier
mentioned law of requisite variety [36], are examples of scientific principles that are
applicableinanenterpriseengineeringcontext.
Architecture principles are commonly seen as normative principles. TOGAF [13]
states that “principles are general rules and guidelines, intended to be enduring and
seldomamended,thatinformandsupportthewayinwhichanenterprisesetsaboutful-
fillingitsmission”.Theuseofprinciplesinthecontextofenterprisearchitecturecanbe
tracedbacktoamulti-yeardeepdiveresearchprojectledbyMichaelHammer,Thomas
H. Davenport,and JamesChampy, calledthe Partnershipfor Researchin Information
Systems Management (or PRISM) [40], which was sponsored by about sixty of the
largestglobalcompanies(DEC,IBM,Xerox,Texaco,Swissair,JohnsonandJohnson,
PacificBell,AT&T,etcetera).Itisaprinciplesbasedarchitectureframework,alsoin-
volvingcoreterminologyof,whatwasatthatstage,anovelparadigm.Inthiscontext,
principlesweredefinedas“simple,directstatementsofanorganisation’sbasicbeliefs
abouthowthecompanywantstouseITinthelongterm”.Notethatinthisdefinition,the
operativewordiswants.Itreferstothefactthatfundamentally,suchprinciplesareused
to express a normative desire. Even more, it also expresses how these principles will
aimtobridgethecommunicationgapbetweentopmanagementandtechnicalexperts.
ThePRISMmodel,beingfrom1986,isamongthefirstpublishedenterprisearchitec-
tureframework,andassuchactuallyprecedestheZachmanframework[41](published
oneyearlater).PRISM’sconceptofprinciplesaswellashowtheyguidethedefinition
andevolutionofarchitectureswasitsmostsalientandwidelyacceptedcontribution.
ThePRISMmodelhasstronglyinfluencedotherenterprisearchitecturestandards,
methods and frameworks. The earliest publications referring to the concept of prin-
ciple, in an enterprise architecture context, can indeed be traced back to the PRISM
project [31, 32]. Furhermore, the HP Global Method for IT Strategy and Architec-
ture[34,42],whichisbasedonworkatDigitalEquipmentCorporationstartingin1984,
wasalmostcompletelybasedonthePRISMmodelandtheconceptofprinciples.Many
yearslater,thePRISMreport[40]alsoinfluencedtheIEEEdefinitionofarchitecture,
asmanyoftheIEEE1471[27]committeemembers(Digitalincluded)wereemployed
bytheoriginalsponsorsofthisearlywork.Theconceptofarchitectureprincipleasit
isdefinedinTOGAF[13]today,isalsoinspiredbythePRISMmodel.
Normativeprinciplesdonotexistinisolation.Theyarebasedonallsortsofother
artefacts, such as the strategy, issues, the existing environment and external develop-
ments.Ontheotherhand,theyalsoinfluenceallsortsofotherartefacts,suchasguide-
lines,requirements,designsandimplementations.Onecanregardthenormativeprin-
ciples as bridging between strategy and operations; they are primarily an alignment
instrument. They are formulated based on knowledge, experience and opinions of all
sortsofpeopleintheorganisations;seniormanagement,aswellasthepeoplethatdo
6 H.A.ProperandD.Greefhorst
the actual work. This mixture of people is also the target audience of normative prin-
ciples. In that sense, the definitions of normative principles also provides a common
vocabularyfortheorganisation.
3.3 Credosversusnorms
Inpracticeweseenormativeprinciplesatvariouslevelsofprecision.In [24]wehave
madethedistinctionbetweenarchitectureprinciplesandguidelines,whereguidelines
aremorespecificthanarchitectureprinciples.NORA[43]distinguishesbetweenfunda-
mentalprinciplesandderivedprinciples,wherefundamentalprinciplesarethebasisfor
derivedprinciples.Thelevelofprecisioninfluencestheabilitytoassessthecompliance
of a design or architecture to the principle. When considering the role of principles
bridging between strategy, via architecture to design, this is quite natural. At first, a
principlewillbeformulatedratherinformallyandrefinedlateroninordertouseitas
a means to restrict design freedom. The definition of the word principle in the dictio-
nary[35]suggestsmultipleformsofprinciples:
– 1a:acomprehensiveandfundamentallaw,doctrine,orassumptionb(1):aruleor
code of conduct (2): habitual devotion to right principles <a man of principle> c:
thelawsorfactsofnatureunderlyingtheworkingofanartificialdevice,
– 2:aprimarysource:origin,
– 3a:anunderlyingfacultyorendowment<suchprinciplesofhumannatureasgreed
andcuriosity>b:aningredient(asachemical)thatexhibitsorimpartsacharacter-
isticquality,
– 4:ChristianScience:adivineprinciple:god.
In terms of the general definition, scientific principles refers to the interpretation of
principlesaslawsorfactsofnatureunderlyingtheworkingofanartificialdevice,nor-
mativeprinciplesreferstoprinciplesinthesenseofaacomprehensiveandfundamental
law,doctrine,orassumptionoraruleofconductthatguidechangesintheenterprises
byinfluencing/directingthedesignofthesechanges.
Atthestartoftheirlife-cycle,normativeprinciplesarejuststatementsthatexpress
theenterprise’sfundamentalbeliefofhowthingsoughttobe.Atthisstage,theirexact
formulationislessrelevant.ThisisinlinewithintentionsbehindTOGAF[13]andthe
Zachman[41]framework,wherethearchitectureprocessstartswiththecreationofan
architecturevision.Inthisphase,architectureisveryfuture-orientedandmostlyacre-
ativeprocess.Theprinciplescanbeusedasameanstoexpressavision,whichismostly
basedonpersonalbeliefsofthestakeholdersinvolvedintheenvisioning.Theycanbe
seen as normative principles in their initial stage. They are not yet specific enough to
actuallyusethemasanorm.Inotherwords;assessingcomplianceofarchitecturesand
designstotheseprinciplesisnotfeasible.Theyareprimarilyusedasasourceofinspi-
ration.Examplesofprinciplesinthisphase,takenfrompracticalcases,are:
– Weshouldfollowcitizenlogic.
– Workanywhere;anytime.
– Reuseasmuchaspossible.
– Applicationsshouldbedecoupled.
TheRolesofPrinciplesinEnterpriseArchitecture 7
Principles in this phase can best be referred to as being a credo. The dictionary [35],
definescredoas:“asetoffundamentalbeliefs;also:aguidingprinciple”.Thisisvery
close to the definition of principle by Beijer [34]: “A fundamental approach, belief,
or means for achieving a goal...”. In terms of the dictionary definition of principle,
weconsiderthistocorrespondtoitsinterpretationasacomprehensiveandfundamen-
tal law, doctrine, or assumption. As such, credos are things an enterprise consciously
choosestoadopt.Theyrepresentthefundamentalbeliefsorassumptionsunderpinning
furtherarchitecturaldecisions.Thisallowsenterprisestoprovideafirstelaborationof
anenterprise’sstrategytowardsthedesireddesignoftheenterprise.
Whenenterpriseswanttousenormativeprinciplesasawaytoactuallylimitdesign
freedom, the principles need to be more specific. This is when the exact formulation
of the principle becomes important. They need to be formulated in such a way that
compliance to them can be assessed. This starts with a reformulation of the principle
statement,butextendstootherproperties.Thefullspecificationwilla.o.needtocontain
definitionsofterminologyused,aswellasadefinitionofhowtoassessthecompliance
of a design to the principle. The examples given previously could be reformulated as
followstomakethemmorespecific:
– Thestatusofcustomerrequestsisreadilyavailableinsideandoutsidetheorganiza-
tion.
– Allworkersareabletoworkinatime,locationandenterpriseindependentway.
– Beforebuyingnewapplicationservices,itmustbeclearthatsuchservicescannotbe
rented,andbeforebuildingsuchapplicationservicesourselves,itmustbeclearthat
theycannotbepurchased.
– Communicationbetweenapplicationserviceswilltakeplaceviaanenterprise-wide
applicationservicebus.
Once normative principles have been (re)formulated specific enough to use them
to restrict design freedom, we can refer to them as a norm. The dictionary [35], de-
finesa normas: aprinciple ofright actionbinding uponthe membersof agroup and
servingtoguide,control,orregulateproperandacceptablebehaviour.Intermsofthe
dictionarydefinitionofprinciple,weconsiderthistocorrespondtoitsinterpretationas
rule of conduct. Norms can also be regarded as a tactic by which a credo can be en-
forced.Toindeedenablethenormativeeffectofnorms,theyarerequiredtobespecific,
measurable,attainableandrelevant.
WhenconsideringTOGAF’s[13,Section3.17]definitionofprinciple:
Aqualitativestatementofintentthatshouldbemetbythearchitecture.Hasat
leastasupportingrationaleandameasureofimportance.
andmorespecificallythepurposeitattributestosuchprinciples[13,Section36.2.4]:
Principlesaregeneralrulesandguidelines,intendedtobeenduringandsel-
dom amended, that inform and support the way in which an enterprise sets
aboutfulfillingitsmission.
we take the stance that TOGAF requires/presumes architecture principle to be in the
formofnorms.
8 H.A.ProperandD.Greefhorst
3.4 Principlesversusrequirementsandinstructions
Normativeprincipleslimitdesignfreedom.Theyare,however,nottheonlystatements
which limit design freedom. Requirements also limit design freedom. However, re-
quirements state what (functional or constructional) properties a (class of) system(s)
shouldhave,andwhythestakeholderswantthe(classof)systemstohavetheseprop-
erties (also see [34]). Normative principles provide policies on how the design of the
(class of) system(s) will ensure that the actual implemented system(s) will meet the
requirements.Requirementsarethebasisforsolutions,expressingtheirrequiredchar-
acteristics. Fisher [9] states that architecture principles refer to the construction of an
enterprisewhilerequirementsrefertoitsfunction.
Generally,enterprisearchitecturesarenotonlyspecifiedintermsofnormativeprin-
ciples,butalsointermsofmoreinstructivestatements,suchasmodelsanddetailedde-
scriptionsonhowtoapplytheseinaspecificsituation.Wewillrefertothesestatements
asinstructions,sincetheytelldesignersspecificallywhattodoandwhatnottodo.In-
structions will refer to the concepts used in the actual construction of the enterprise,
suchas:valueexchanges,transactions,services,contracts,processes,components,ob-
jects,buildingblocks,etcetera.EnterprisestypicallyuselanguagessuchasUML[44],
BPMN [45], TOGAF’s [13] content framework, ArchiMate [3], or the language sug-
gested by the DEMO method [28], to more explicitly express their architectures in
terms of concrete modelling concepts. Instructions, provide a more operational and
tangiblerefinementofthenormativeprinciples.Duetotheirtangiblenature,interms
ofactualconceptsusedintheconstructionoftheenterprise,architecturemodelsenable
enterprises to study/analyse the effects of different options for the future, as well as
analyseproblemsinthecurrentsituation[2].Justasnormativeprinciples,instructions
arerequiredtobespecific,measurable,attainableandrelevant
Collectivelywewillrefertonormativeprinciplesandinstructionsasdirectivesto
express the fact that they both direct the design of the enterprise (albeit at different
levelsofspecificity)andbothinvolveachoicebytheenterprisetodirecttheirtransfor-
mation.Thedictionary[35]definesdirectiveas:servingorintendedtoguide,govern,
orinfluence,whiletheOMG’sbusinessmotivationmodel[46]alsousesthenotionof
directiveasthemostgeneralformofguidance/regulation.IntermsoftheNAFdefini-
tionofarchitecture[14],thesetwoflavoursofdirectivecollectivelycoveritsroleasa
normativerestrictionofdesignfreedom.
Figure1provides(inthestyleofObjectRoleModelling[47])adomainmodelpo-
sitioningcredos,norms,normativeprinciples,instructions,requirementsandscientific
principles.IntheORMdiagram,theencircledcrossisusedtosignifythefactthatcre-
dos,norms,scientificprinciples,instructionsandrequirementsaremutuallyexclusive.
Thegeneralnotionofpropositionisusedasafurthergeneralisationofscientificprinci-
ples,requirementsanddirectives.Eachpropositionmusthaveaqualityandadefinition
(signifiedbytheblackdotinthediagram),whiletheyhaveatmostonedefinition(sig-
nifiedbytheshortbaronthefacttype).
TheRolesofPrinciplesinEnterpriseArchitecture 9
has / of
Definition
(description)
has / of
Proposition Quality
(name) (name)
{ specific, measurable, attainable,
relevant, time-bound }
Scientific
Directive Requirement
principle
underpins /
is underpinned by
Normative
Instruction
principle
operationalised by /
operatonalises
Credo Norm
enforced by /
enforces
A Credo must have Qualities: { attainable, relevant, time-bound }
A Norm must have Qualities: { specific, measurable, attainable, relevant, time-bound }
A Instruction must have Qualities: { specific, measurable, attainable, relevant, time-bound }
A Scientific principle must have Qualities: { specific, measurable }
A Requirement must have Qualities: { specific, measurable, attainable, relevant, time-bound }
Fig.1.Coreterminology
10 H.A.ProperandD.Greefhorst
3.5 Architectureprinciplesversusdesignprinciples
Regardinganarchitectureasanormativerestrictionofdesignfreedom,raisestheques-
tionwhatthedifferenceisbetweenarchitectureanddesign.Moreoperationally,What
shouldbeincludedinanarchitecture,andthusrestrictthefreedomofensuingdesign
activities,andwhatshouldindeedbelefttodesigners?AssuggestedbytheIEEE[27]
andTOGAF[13]definitionsofarchitecture,thearchitecturelevelshouldfocusonfun-
damentalaspects.Anenterprisearchitectureshouldprovideanelaborationofanenter-
prise’sstrategy,whilefocussingonthecoreconcernsofthestakeholders.Assuch,an
architectureistypicallypositionedatalevelconcernedwithaclassofsystems.Ade-
signfocusesontheremainingrequirementsanddesigndecisionspertainingtoaspecific
systembeingdeveloped,whichwilltypicallyhavealimitedimpactonthekeyconcerns
ofthestakeholders.
Fehskens[37]statesthatarchitectureshouldexplicitlyaddressalignment,relating
theroleofarchitecturetothemission.Heredefinesarchitectureas“thosepropertiesof
athinganditsenvironmentthatarenecessaryandsufficientforittobefitforpurpose
foritsmission”.Inhisview,architectureshouldfocusonwhatisessential,on“thestuff
that matters”. This equates to those properties that are necessary and essential. This
is also what distinguishes architecture from design. A different architecture implies a
differentmission,whilstdifferentdesignsmayaddressthesamemission.
Rivera[42]acknowledgesthatarchitectureisabouttheessense.Headdsthatgen-
erally speaking, design work seeks to find optimal solutions to wellunderstood prob-
lems.It’smoresciencethanart,algorithmicinnature,anddealsmostlywithasystem’s
measurableattributes.Architectingdealsprimarilywithnonmeasurableattributesusing
nonquantitativetoolsandguidelinesbasedonpracticallessonslearned.Inhisview,the
architectureusesaheuristicapproach.Whereasdesignandengineeringworkisprimar-
ilydeductiveinnature,architectureworkisprimarilyinductive.
The distinction between design and architecture, also allows us to distinguish be-
tween architecture and design versions of normative principles, instructions and re-
quirementsrespectively:
– Architectureprinciplesarenormativeprinciplesthatareincludedinthearchitecture
ofaclassofsystems.
– Architecture instructions are instructions that are included in the architecture of a
classofsystems.
– Architecturerequirementsarerequirementsthatpertaintothearchitectureofaclass
ofsystems.
– Designprinciplesarenormativeprinciplesincludedinthedesignofaspecificsystem.
– Designinstructionsareinstructionsthatareincludedinthedesignofaspecificsys-
tem.
– Designrequirementsarerequirementsthatpertaintothedesignofaspecificsystems.
The role of these concepts is made even more explicit in Figure 2. In this diagram,
conceptsfromFigure1areshownintheirarchitectureanddesignvariants,andguided
byscientificprinciples.Thediagramillustratestheflowfromstrategyviarequirements
thatshouldalreadybeaddressedatthelevelofthearchitecture,theactualarchitecture,
therequirementstobemetbythedesignofthesystem,thedesignofthesystem,tothe